Life Cycle of Stars/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby. An animation shows a starry sky. It pans downward to show Moby looking at a star map behind Tim. An image shows Tim's hand holding a printed letter. TIM: Dear Tim & Moby, how do stars burn out? From Corey. This is one of my favorite topics. Stars change throughout their lives just like we do — only they live for billions of years instead of a few decades! An animation shows four circles representing stars in succession from the top left of the screen to the bottom right of the screen on a black background. The first is a small star that is purple with a yellow outline that fades into the background as it moves outward from the circle. The second is a medium star that is yellow with a yellow outline that fades into the background as it moves outward from the circle. The third is a large star that is red with a red outline that fades into the background as it moves outward from the circle. The fourth star is roughly the same size as the first star. It is white and has a yellow outline that fades into the background. TIM: They start out as clouds of gas and dust called stellar nurseries. The image changes to show dark purple clouds on a black background. Text reads: stellar nursery. TIM: The force of gravity slowly pulls particles inside these clouds closer together, causing dense clumps to form. An animation shows three white circles representing clouds of condensed particles forming. Shapes move toward these condensed particle clouds to illustrate the condensing particles. The clouds slowly get larger and larger. Text reads: stellar nursery. TIM: If a clump grows large enough, the pressure caused by gravity inside one of these baby protostars begins to generate heat. The animation zooms in on the largest cloud. Shapes continue to move toward it to illustrate the condensing particles. The cloud gains a yellow outline that blends into the purple background as it moves outward. Text reads: protostar. TIM: This heat and pressure build until nuclear fusion reactions begin to take place in the core. Gravity pulls hydrogen atoms together, smashing and fusing them into heavier helium atoms. An animation magnifies a cross section of the cloud. Several purple circles representing atoms float around in a yellow circle. Each has one smaller circle at its center. As the animation continues, some of these atoms collide with others causing an explosion and forming larger atoms. These larger atoms have two connected circles in their centers. Text reads: nuclear fusion. TIM: Nuclear fusion generates an enormous amount of energy, causing the star to ignite. The animation zooms back out to the whole cloud. The yellow outline begins to pulsate. The cloud then turns yellow with some orange lines interspersed throughout. Then, with an explosion, the yellow cloud becomes a circular star and turns a lighter shade of yellow. The yellow outline continues to pulsate. TIM: This is the beginning of the longest part of the star’s lifetime, or its main sequence. The scene changes back to Tim and Moby. Text reads: main sequence. TIM: That's where our star, the sun, is right now. An animation shows a field with a bush in it. The sun is bright in the background. The animation moves to zoom in on the sun. TIM: It's about 4 point 6 billion years old, which means it's a little less than halfway through its 10 billion-year-long main sequence. An animation shows Earth, Venus, and Mercury orbiting around the sun with stars in the background. Earth rotates as the moon, also rotating, orbits around it. The sun pulsates in the background. MOBY: Beep? The scene changes back to Tim and Moby. TIM: Well, what happens to a star after its main sequence depends on its mass. Astronomers actually don't know what happens to low-mass stars — those with less than about half the mass of our sun. They may actually have a main sequence that lasts more than a trillion years. That’s longer than the current age of the universe! An animation shows a blue circle that represents a star on a background with white dots that represents other stars. It pulsates. TIM: Mid-sized stars, like our sun, become white dwarfs. The scene changes back to Tim and Moby. Moby is looking at a star map. Text reads: white dwarf. TIM: Those are super-dense objects about as massive as the sun but only a fraction as big — they're around the size of the Earth, actually. An animation shows a small white circle representing a star. It has a yellow outline and pulsates. Text reads: white dwarf. TIM: A couple of things'll happen before the sun turns into a white dwarf, though. The scene changes back to Tim and Moby. TIM: The sun will begin to die when it uses up all the hydrogen in its core. An animation shows Earth, Venus, and Mercury orbiting around the sun with stars in the background. Earth rotates as the moon, also rotating, orbits around it. The sun pulsates in the background. TIM: At that point, the sun will expand, ballooning to many times its current size. Stars in this stage of their life are called red giants because their surfaces cool down to a red glow. Plus they're really, really big. The animation of Earth, Venus, and Mercury orbiting the sun continues. The sun begins to get larger as it pulsates. It becomes redder and larger as the animation continues. Eventually, Mercury is burned up and explodes when the sun overtakes it, leaving only Earth and Venus. Text reads: red giant. TIM: The sun will start burning helium at that stage, fusing it into even heavier elements. An animation shows large purple circles with two smaller connected circles in the middle that represent atoms. These atoms collide with each other to form larger atoms with four circles in the center. TIM: Eventually, it may get so big that it engulfs the earth! The animation of Earth and Venus orbiting around the sun in its red giant phase continues. The sun continues to pulsate and expand. Eventually Venus is burned up and explodes, and finally Earth is burned up and explodes as the sun fills the whole screen. MOBY: Beep! TIM: Oh, don't worry. We’ll all be long gone before that happens. It's billions of years away! The scene changes back to Tim and Moby. TIM: Anyway, after no more than about a billion years as a huge red giant, the sun will begin to collapse under the pressure of gravity. An animation shows the sun in its red giant phase. It is represented by a large pulsating red circle on a black background with white dots, representing other stars. TIM: It'll actually get kind of unstable, expanding and contracting and shedding its outer layers in the process. The remains of those outer layers form a big cloud of gas and dust called a planetary nebula The animation continues to show the sun in its red giant phase pulsating and contracting to smaller and smaller sizes. It leaves behind purple clouds around it as it gets smaller. Eventually, the sun is shown as a small white circle in the center of a circular cloud of gas. Text reads: planetary nebula. MOBY: Beep? TIM: Nope, they don't have anything to do with planets. They're just called that! The scene changes back to Tim and Moby. Tim: But you know, you’ve probably seen some awesome pictures of planetary nebulas from the Hubble Space Telescope. These are pictures of stars that are at the end stages of their lives. The scene changes to show four images of different planetary nebulas. The first is shaped like an eye. It has blue and orange clouds surrounding a white dot in the center. The second looks like butterfly. It has red, orange, and purple clouds surrounding a while dot in the center. The third looks like an ellipse. It has light blue clouds with a yellow outline surrounding a white dot in the center. The fourth is circular. It has blue and pink clouds surrounded by some orange clouds, all surrounding a white dot in the center. TIM: It's kinda like watching what'll happen to our sun way before it actually does! The scene changes back to the sun being shown as a small white circle in the center of a circular purple cloud of gas. It pulsates. TIM: Anyway, at the center of a planetary nebula is a core of carbon, which, after cooling, finally becomes a white dwarf. An animation shows a small white circle pulsating. The pulsating eventually stops. The white circle remaining represents a white dwarf and has a yellow outline. MOBY: Beep. TIM: Well, that’s the route our sun'll take, but it’s not the only way a star can die. The scene changes back to Tim and Moby again. TIM: Stars much bigger than our sun collapse so quickly that they explode into a supernova scattering stellar material far and wide. An animation shows a red circle, representing a large star, pulsating. The star collapses inward rapidly to become very small. Then a shockwave erupts from it as it explodes, sending particles in every direction. A small orange circle represents what is left of the star and a purple cloud surrounds it, pulsating. Text reads: supernova. TIM: A supernova explosion can last for a month or longer, and during that time it can be as bright as a galaxy with a billion stars! The scene changes to a view of the night sky. There are many distant stars, and one is pulsating with flashes of light to indicate a supernova. TIM: The clouds of gas and dust a supernovas spew out are where heavy elements are made — and they lead to the formation of new stars! The scene changes back to the cloud surrounding what is left of a star after it explodes in a supernova. An animation shows several white circles representing clouds of condensing particles. Shapes move toward them to represent particles condensing. TIM: The core that's left over can go one of two ways, depending on the mass of the original star. The image zooms in on the core of the old star at the center of the cloud, a white circle on a black background with smaller white dots, representing other stars. TIM: If the star's about 10 times as massive as our sun, the protons and electrons in the core are crushed into neutrons. What you get is a neutron star. An animation shows a zoomed-in cross section of the core of the old start. Two circles, a smaller one labeled "e" and a larger one labeled "Upper P" collide to form a single larger circle labeled "Upper N". The animation concludes as a yellow outline surrounds the core of the old star. Text reads: neutron star. TIM: Some neutron stars spin rapidly, emitting pulses of radio waves. These are known as pulsars. An animation shows a small blue circle representing a neutron star. The neutron star is spinning rapidly. Large, thin, white circles that represent radio waves emanate from the star as it spins. A tone sounds as each radio wave leaves the star. Text reads: pulsar. TIM: If, on the other hand, the original star was more than 10 times as massive as the sun, its supernova core will collapse in on itself. It will keep collapsing until it forms a tiny area of infinite density called a singularity. The scene changes back to the cloud surrounding what is left of a star after it explodes in a supernova. An animation shows the core getting smaller and smaller until it is disappears and is replaced with a black circle surrounded by white and purple beams of light. Text reads: singularity. TIM: We call this a black hole, and its gravity is so powerful that nothing within range can escape it. Text reads: black hole. Moby: Beep. TIM: Nope, not even light. An animation shows the labels "singularity" and "black hole" getting sucked into the black hole. Then the scene zooms in on the center of the black hole and fades to black. TIM: And nothing you throw into a black hole will ever come back. The scene changes back to Tim and Moby. TIM: We actually have a whole other movie on those, so you should go check it out. Well, time to take the trash out. Moby grabs a trash can and looks at it. He turns on his rocket feet and flies into the sky as Tim looks on. TIM: You know, we could just take the trash out to the corner. Moby flies to a black hole and begins throwing bits of trash from the trash can at the black hole, which sucks them in. MOBY: Beep. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts